A method for manufacturing an optical waveguide includes shaping a substrate of organic material, applying at least one intermediate layer by a first vacuum coating process onto the substrate and applying a waveguide layer by means of a second vacuum coated process onto the intermediate layer. The at least one intermediate layer is applied so that only a negligible part of light energy reaches an interface surface between the intermediate layer and the substrate.
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1. A method of manufacturing an optical waveguide comprising the steps of:
(a) shaping a substrate consisting essentially of organic material only; applying at least one intermediate layer by a first vacuum coating process onto the substrate; and (c) applying a waveguide layer by means of a second vacuum coating process onto the intermediate layer; (d) said at least one intermediate layer being applied so that only a negligible part of light energy reaches an interface surface between said intermediate layer and said substrate.
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(a) TiO2, TaO5, ZrO2, Al2O3, SiO2--TiO2, HfO2, Y2O3, Nb2O5, silicon nitride, oxynitride SiOxNy, HfOxNy, AlOxNy, TiOxNy, TaOxNy and MgF2, CaF2, (b) silicone, SiOx, Ge, GaAs, GaAlAs.
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This is a division of application Ser. No. 08/751,369, filed Nov. 19, 1996, now U.S. Pat. No. 6,610,222 which is a continuation of Ser. No. 08/278,271 filed Jul. 21, 1994, now abandoned which claimed priority on Swiss application 02 255/93-5, filed Jul. 26, 1993, which priority claim is repeated here.
The present invention concerns a waveguide, a process for producing a waveguide, and further use of an intermediate layer on a waveguide and use of an organic substrate as a carrier substrate on a waveguide.
For many uses, for example sensors, integrated optics and the like it is desirable to have planar waveguides available. As shown in
For many uses at least one of those layers must be structured. In order for light to be coupled at all into the waveguide, the method which is in fact the most elegant method involves providing the waveguide with a structure 4--a grating--, as shown in
It is immaterial whether the grating 4 is provided at the substrate surface or in or at the waveguide layer.
In addition it is often desirable for the waveguide to be spatially structured as a whole.
As waveguides of that kind are usually constructed on a glass substrate, the structuring procedures employed are photolithographic methods and the following etching methods: ion milling, reactive ion etching, wet-chemical etching and the like.
Such structuring procedures are time-consuming and expensive.
In addition waveguides on a glass substrate can only be shaped with difficulty and they are sensitive in regard to mechanical stresses such as impact stresses.
The substrate/waveguide layer/environment interaction but in particular the substrate/waveguide layer interaction which is relevant here substantially determines the waveguide property.
The problem of the present invention is to propose a waveguide:
a) in which structuring is substantially simpler and therefore less expensive and which possibly
b) is deformable within limits and/or
c) is less sensitive to mechanical stresses and/or
d) whose substrate can be used flexibly together with different waveguide layers and materials.
This is achieved in a waveguide of the kind set forth in the opening part of specification by the configuration set forth in the the claims.
Particularly when using a polymer, such as for example and as is preferred nowadays a polycarbonate, as the waveguide substrate, it is now very much cheaper to structure the waveguide in particular as a whole, whether this is done by embossing, deep-drawing, injection moulding and the like, and then in particular to provide the coating with a wave-conducting material. In that respect it is found that the application of a wave-conducting material to a substrate of organic material, in particular a polymer, is in no way trivial. It is observed in particular that the losses of a waveguide produced in that way, that is to say waveguide layer directly on the substrate, defined as a drop in terms of intensity with a given mode and a given wave length over a certain distance, are substantially higher, at least by a factor of 10, than when an inorganic material such as for example glass is used as the substrate material.
To our knowledge the problem involved here is substantially new territory. Admittedly there are indications in the literature, for example in "Design of integrated optical couplers and interferometers suitable for low-cost mass production", R. E. Kunz and J. S. Gu, ECIO 93-Conferenz in Neuchátel, that integrated optics could be inexpensively made from structured plastics material, but such reports can only document an existing need.
It is self-evident however that on the one hand all structuring procedures for organic materials, in particular polymers, and on the other hand coating processes such as CVD, PECVD, including vapour deposit, sputtering, ion plating, etc., belong to the state of the art. In that respect coating of plastics parts, for example spectacle lenses, reflectors etc. with very different materials also belongs to the state of the art, for example including by means of plasma polymerisation.
Attention should further be directed to the theory of planar waveguides in "Integrated Optics: Theory and Technology", R. G. Hunsperger, Springer Series in Optical Sciences, Springer-Verlag 1984.
The invention, in regard to its various aspects, with preferred embodiments also being the subject-matter of the further claims, is described hereinafter by means of Examples and Figures.
In that respect in the Figures which have already been in part described:
To explain the realisation which is the underlying basis of the invention
wherein {overscore (r)} denotes the radius vector.
It will be seen therefrom, looking back at
While wave-conducting layers on glass, for example on Corning 7059 overall have very low losses or a very low level of absorption, the losses of the same wave-conducting layers on organic material as a substrate material, such as in particular polymer substrates, for example on polycarbonate substrates, are higher at least by a factor of 10, in dependence on the thickness of the waveguide layer 1 and accordingly the percentage proportion of energy which occurs in the substrate material but in particular at the substrate/waveguide interface.
In that respect the above-mentioned increase in losses is not only a consequence of the respective coating process specifically employed but also a consequence of the interaction, discussed with reference to
In accordance with the invention, the intermediate layer 8 and possibly an intermediate layer system 8 provides that light intensity I in the waveguide is low where the general loss coefficient α is high, whereby the losses are minimized. That is achieved by providing for a suitable configuration of the refractive index profile on the waveguide normal to the surface thereof.
Materials
1. Materials for the Wave-conducting Layer 1:
The following are preferably used in particular for the wavelength range of 400 nm to 1000 nm:
TiO2, Ta2O5, ZrO2, Al2O3, SiO2--TiO2, HfO2, Y2O3, Nb2O5, silicon nitride, oxynitride (SiOxNy, HfOxNy, AlOxNy TiOxNy, TaOxNy) and MgF2, CaF2.
For wavelengths >1000 nm silicon, SiOx, Ge, GaAs and GaAlAs preferably fall to be considered.
2. Substrate:
Organic materials, in that respect in particular polymers such as polycarbonate, PVC, polymethylmethacrylate (PMMA), and PET.
3. Material of the at Least One and Preferably the One Intermediate Layer 8:
Inorganic dielectric materials, in particular oxides, nitrides, carbides and the mixed forms thereof such as in particular SiO2, Si3N4, more generally SiOxNy, and mixed materials, in particular with an SiO2-component, an Si3N4-component or, more generally, an SOxNy-component.
4. Cover:
All known techniques with exposed waveguide layer or waveguide layer covered with a cover layer.
Processing Procedures:
1. Application of the Waveguide Layer
Preferably vacuum coating processes are used for this purpose, in particular plasma-enhanced CVD-processes (PECVD), CVD-processes, reactive PVD-processes, in particular reactive vapour deposit, sputter coating and ion plating. The plasmas used are DC- or AC-fed, which includes low-frequency HF- and microwave plasmas and DC+AC-mixed forms. It is also possible to use non-vacuum coating processes such as for example dip drawing and spin coating.
Having regard to the fact that the at least one wave-conducting layer 1 is to be applied to the substrate material used in accordance with the invention, coating processes are preferably used in which the substrate temperature is lower than the softening temperature of the substrate material employed, in particular <100°C C., preferably <60°C C.
2. Application of the at Least One Intermediate Layer:
The same methods are used as for applying the waveguide layer, with the same limitations in regard to substrate temperature control. It is additionally possible to use plasma polymerisation if for example a silicon-containing monomer is used for the layer deposit operation.
3. Substrate:
The substrate of organic material, by far and away preferably a polymer, is shaped by means of a process which is known for processing plastics material. That includes in particular embossing, deep drawing, injection moulding and blow moulding (for PET-plastics).
Besides the optical function, namely providing for light intensity at an optimum low level in substrate material or at a substrate/layer interface, with a high level of absorption, the intermediate layer used in accordance with the invention or a layer of the intermediate layer system used in accordance with the invention acts as a bonding layer between the substrate on the one hand and the superposed layers. It is entirely possible to provide, towards the waveguide layer, a first intermediate layer which principally provides the desired optical insulation effect, and to solve the adhesion problem by means of a further intermediate layer, bearing against the substrate.
The losses at a waveguide according to the invention are of the same order of magnitude as the losses on conventional waveguides of glass substrate, and are in particular less than 100 dB/cm, preferably less than 50 dB/cm and in particular even lower than 10 dB/cm.
Moreover a fact of extraordinary importance is that the provision of the intermediate layer 8 in accordance with the invention, as shown in
As was made clear, the structurings shown by way of example in particular in
In regard to establishing the refractive index or the refractive index variation by way of the intermediate layer which is provided in accordance with the invention, corresponding to its thickness dimension DZS, there are various possible alternatives, as can be seen from these Figures. In most cases the refractive index of the intermediate layer is chosen to be lower than that nF of the waveguide layer. As is clear from
In this respect,
When a layer of inorganic material, more specifically waveguide layer material, is directly applied to an organic substrate material, in particular a polymer material, there is a high level of probability that reactions occur between components of the polymer and those of the applied wave-conducting layer. There is a high level of probability that this reaction results in a high-absorption transitional phase. This is if the waveguide were applied directly to a polymer substrate.
In accordance with the invention however, because of the similarity between the inorganic intermediate layer material and the waveguide layer material, such an interface reaction occurs to a much lesser degree, and any interface reaction between the intermediate layer material and the substrate material results only in low losses because the intermediate layer ensures that only low light energy values lead to losses at all at that interface.
Therefore the intermediate layer according to the invention does not suppress the above-mentioned interface reaction at the substrate surface, but in practice a glass intermediate layer is simulated between the substrate and the waveguide layer. Unwanted surface roughnesses at the substrate used in accordance with the invention are smoothed out to a certain degree by the provision of the intermediate layer according to the invention, in dependence on the coating parameters.
A waveguide with the refractive index profile was produced in principle as shown in
Process Parameters for TiO2-waveguide on a PC7-substrate with an SiO2-intermediate Layer:
Intermediate Layer Coating Process:
Sputter coating with plasma production from a DC-source whose output is temporarily cyclically separated from the plasma discharge section and the latter is temporarily short-circuited.
Target:
Target: | Ak525; SiS23379 |
Magnetron: | MC-525 |
Distance between target and substrate: | 70 mm |
DC-source: | 10 kW |
Vacuum chamber: | BAK-760 S |
Argon pressure: | pAr = 4E-3 mbar |
Set discharge power: | p = 6 kW |
DC-voltage in the metal mode: | Usb = -695 V |
DC-voltage in the transition mode: | Usb = -595 V |
Argon flow: | qAr = 58.8 sccm |
O2-flow: | qO2 = 47 sccm |
SiO2-layer thickness: | varying as shown in |
Sputter rate: | R = 0.28 nm/s |
Production of the waveguide layer: | By means of sputtering as |
for the production of the | |
intermediate layer. | |
Target: | Ak525; TI92-421/1 |
Magnetron: | MC-525 |
Distance target/intermediate | 70 mm |
layer-coated substrate | |
DC-source: | 10 kW |
Vacuum chamber: | BAK-760 S |
Argon pressure: | pAr = 4E-3 mbar |
Plasma discharge power: | P = 6 kW |
DC-voltage in the metal mode: | Usb = -531 V |
DC-voltage in the transition mode: | Usb = -534 V |
Argon flow: | qAr = 57.4 sccm |
Oxygen flow: | qO2 = 17 sccm |
Thickness of the TiO2-waveguide layer: | 95 nm |
Sputter rate: | R = 0.069 nm/s |
Taking the resulting waveguide, the losses found were about 8 dB/cm in the TM-mode and at a wavelength of 633 nm, with a thickness d SiO2 of 20 nm.
It is therefore also proposed that preferably the intermediate layer should be provided in accordance with the invention with a thickness of <10 nm, and in that respect, as will be readily apparent, as thin as possible in order to minimise the production costs, that is to say preferably about 10 nm.
Rudigier, Helmut, Edlinger, Johannes
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